An example of a conventional image matching system is described in Tsutada etc., “Dictionary configuration method for discriminating person independently of face direction,” The Transactions of the Institute of Electronics, Information and Communication Engineers, D-II, Vol. J78-D-II, No. 11 (1995), pp. 1639-1649 (hereafter referred to as first conventional technique). As shown in FIG. 26, an image matching system according to the first image matching system includes an image input section 10, an image matching section 40, a result display section 80, a reference image storage section 70, and a reference image registration section 75.
The conventional image matching system having such a configuration operates as hereafter described.
Reference images of various objects (such as reference face images of persons) picked up are previously stored in the reference image storage section 70 by the reference image registration section 75. However, reference images greatly change depending on the condition at the time of imaging (conditions such as the pose and illumination). With respect to one object, therefore, a plurality of (a large number of) images imaged under various conditions are previously stored.
The image input section 10 is implemented by using, for example, a camera. The imaged input image is stored in a memory (not illustrated). The image matching section 40 compares the input image obtained from the image input section 10 with each of reference images obtained from the reference image storage section 70, calculates similarities (or distance values) of respective features, and selects a reference image having the greatest similarity (or the shortest distance) for each object. Each image is represented by gray level features. In the calculation of similarity between features and the calculation of the distance value, for example, the normalized correlation and Euclidean distance are used. The result display section 80 displays a reference image of an object having the greatest similarity selected from among the reference images, as a matching result (or displays candidate reference images in the descending order of the similarity).
Another example of a conventional image matching system is described in Japanese Patent Application Laid-Open No. 2000-322577 (hereafter referred to as second conventional technique). As shown in FIG. 28, the conventional image matching system includes an image input section 10, an image conversion section 35, a partial image matching section 45, a result display section 80, a reference image registration section 75, a representative three-dimensional object model storage section 20, and a three-dimensional object model registration section 25.
The conventional image matching system having such a configuration operates as hereafter described.
One or more representative three-dimensional object models obtained from the three-dimensional object model registration section 25 are previously stored in the representative three-dimensional object model storage section 20. As regards a partial region common to the input image obtained from the image input section 10 and each of the reference image obtained from the reference image storage section 70, the image conversion section 35 converts the input image and/or the reference image so as to make the input condition (such as the pose condition) the same by using a three-dimensional object model obtained from the representative three-dimensional object model storage section 20, and thereby generates partial images.
For example, as shown in FIG. 29, the partial region is a feature portion such as an eye, a nose or a mouth. By previously specifying a feature point with respect to each of the images and the three-dimensional object models, correspondence can be taken. The partial image matching section 45 compares the converted input image obtained from the image conversion section 35 with a partial image of each of the reference images, calculates respective average similarities, and selects a reference image having the greatest similarity for each object. The result display section 80 displays an object having the greatest similarity among the reference images, as a matching result.